Detecting a vasoactive agent in the bloodstream

ABSTRACT

A system and method are disclosed for detecting a vasoactive agent in patient&#39;s bloodstream. In one embodiment, an input signal is received that is associated with arterial blood pressure. A change of an arterial blood pressure parameter over time is determined. A vasoactive agent is then automatically detected using the determined change. In another embodiment, a waveform associated with an arterial blood pressure signal can be received. A parameter associated with the received waveform is calculate. Then the calculated parameter can be used to determine the presence of a vasoactive agent. In yet another embodiment, detection of a vasoactive agent in any of the other embodiments can be used in a calculation of a hemodynamic parameter, such as cardiac output, stroke volume, systemic vascular resistance, stroke volume variation, cardiac index, stroke volume index, systemic vascular resistance index, vascular compliance, and vascular tone.

FIELD

The present application relates to arterial blood pressure and, inparticular, to detecting a vasoactive agent using a measurement ofarterial blood pressure.

BACKGROUND

Cardiac output (CO) and Stroke volume (SV) are indicators not only fordiagnosis of disease, but also for “real-time” monitoring of patients.Few hospitals are, therefore, without some form of equipment to monitorone or more of these cardiac parameters. Both invasive and non-invasivetechniques are available.

Most of the techniques used to measure SV can usually be readily adaptedto provide an estimate of CO as well, as CO is generally defined as SVtimes the heart rate HR. Conversely, most devices that estimate CO alsoestimate SV as a sub-step. As is explained in greater detail below,still another cardiac parameter that promises to provide clinicallyimportant information is stroke volume variation SVV. One way toestimate SVV is simply to collect multiple SV values and calculate thedifferences from measurement interval to measurement interval.

One common way to measure SV or CO is to mount some flow-measuringdevice on a catheter, and then to thread the catheter into the subjectand to maneuver it so that the device is in or near the subject's heart.Some such devices inject either a bolus of material or energy (usuallyheat) at an upstream position, such as in the right atrium, anddetermine flow based on the characteristics of the injected material orenergy at a downstream position, such as in the pulmonary artery.

Still other invasive devices are based on the known Fick technique,according to which CO is calculated as a function of oxygenation ofarterial and mixed venous blood.

Invasive techniques have obvious disadvantages. For example,catheterization of the heart is potentially dangerous, especiallyconsidering that the patients typically have a serious condition.Moreover, some catheterization techniques, most notably thermodilution,rely on assumptions, such as uniform dispersion of the injected heat,that affect the accuracy of the measurements depending on how well theyare fulfilled. Moreover, the very introduction of an instrument into theblood flow may affect the value (for example, flow rate) that theinstrument measures.

Doppler techniques, using invasive as well as non-invasive transducers,are also used to measure flow and to calculate SV and CO from the flowmeasurements. Not only are these systems typically expensive, but theiraccuracy depends on precise knowledge of the diameter and generalgeometry of the flow channel Such precise knowledge is, however, seldompossible, especially under conditions where real-time monitoring isdesired.

One blood characteristic that has proven particularly promising foraccurately determining parameters, such as CO, SV, and SVV with minimalor no invasion is blood pressure. Most known blood-pressure-basedsystems rely on the so-called pulse contour method (PCM), whichcalculates an estimate of the cardiac parameter(s) of interest fromcharacteristics of the beat-to-beat pressure waveform. In the PCM,“Windkessel” (German for “air chamber”) parameters (characteristicimpedance of the aorta, compliance, and total peripheral resistance) aretypically used to construct a linear or non-linear, hemodynamic model ofthe aorta. In essence, blood flow is analogized to a flow of electricalcurrent in a circuit in which an impedance is in series with aparallel-connected resistance and capacitance (compliance). The threerequired parameters of the model are usually determined eitherempirically, through a complex calibration process, or from compiled“anthropometric” data, i.e., data about the age, sex, height, weight,and/or other parameters of other patients or test subjects. U.S. Pat.No. 5,400,793 (Wesseling, 28 Mar. 1995) and U.S. Pat. No. 5,535,753(Petrucelli, et al., 16 Jul. 1996) discloses systems that rely on aWindkessel circuit model to determine CO.

PCM-based systems can monitor SV-derived cardiac parameters using bloodpressure measurements taken using a variety of measurement apparatus,such as a finger cuff, and can do so more or less continuously. Thisease of use comes at the potential cost of accuracy, however, as the PCMcan be no more accurate than the rather simple, three-parameter modelfrom which it was derived. A model of a much higher order would beneeded to faithfully account for other phenomena. Many improvements,with varying degrees of complexity, have been proposed for improving theaccuracy of the basic PCM model.

Vasoactive agents (such as vasoconstrictors, vasodilators, andinotropes) have an impact on vascular tone (vascular compliance andresistance), which usually induces changes in blood pressure. As aresult, this could have a negative impact on blood-pressure-basedsystems that measure CO and introduces errors on the measurementparameters, such as CO, SV, SVR and SVV. Vasoactive agents are a groupof bioactive chemicals, which change vasomotor tone through theirinfluence on various peripheral receptors. Most of these agents haveinotropic effects (e.g. norepinephrine) as they bind with receptorspositioned on the surface of the myocardium. Vasoactive drugs generallyaffect stroke volume and heart rate, and, thus, determine cardiac outputand overall cardiovascular function. When vasoactive drugs are present,CO, SV, and SVV measurements are often inaccurate.

SUMMARY

A system and method are disclosed for detecting a vasoactive agent inpatient's bloodstream using arterial blood pressure.

In one embodiment, an input signal is received that is associated witharterial blood pressure. A change of a parameter over time isdetermined. A vasoactive agent is then automatically detected using thedetermined change.

The arterial blood pressure can be measured invasively or non-invasivelyto produce the input signal. Additionally, the vasoactive agent can be avasoconstrictor, vasodilator, or inotrope. Example vasoactive agentsinclude Phenylephrine, Epinephrine, Ephedrine, Nitroprusside,Dobutamine, Nitroglycerin, Hydralazine, Trimethaphan, Norepinephrine,Dopamine, Isoproterenol, Amrinone, Milrinone, and Digoxin, but alsoother vasoactive agents can be detected. Naturally occurring vasoactiveagents can also be detected and include, but are not limited to,adrenaline, noradrenaline, histamine, nitric oxide, adrenocorticotrophin(ACTH), vasopressin, etc.

In another embodiment, a waveform associated with an arterial bloodpressure signal can be received. A parameter associated with thereceived waveform can be calculated. Then the calculated parameter canbe used to determine the presence of a vasoactive agent.

The calculated parameter can be selected from pulse pressure, standarddeviation of pressure waveform, the area under the systolic phase of thearterial pressure waveform (systolic area), the area under the diastolicphase of the arterial pressure waveform (diastolic area), mean arterialpressure, systolic pressure, diastolic pressure, pressure at a specifictime point in each heartbeat, differentiation of pressure with respectto time, time durations of specific phases of the arterial pressurewaveform (systolic phase, systolic rise, systolic decay, diastolicphase, diastolic time constant, . . . etc), heart rate (or pulse rate),measures of the morphological parameters of the arterial pressurewaveform, or a combination thereof.

In yet another embodiment, detection of a vasoactive agent in any of theother embodiments can be used in a calculation of a hemodynamicparameter, such as cardiac output, stroke volume, systemic vascularresistance, stroke volume variation, pulse pressure or systolic pressurevariations, cardiac index, stroke volume index, systemic vascularresistance index, vascular compliance, and vascular tone. Such acalculation using the information of the vasoactive agent provides asignificant advantage over prior calculations, which neglect the use ofthe vasoactive agent.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example system diagram illustrating different componentsthat can be used for detecting a vasoactive agent in a patient'sbloodstream.

FIG. 2 is a flowchart of a method for detecting a vasoactive agent in apatient's bloodstream.

FIG. 3 is a more detailed flowchart of an embodiment for detecting avasoactive agent.

FIG. 4 is a flowchart of another embodiment for detecting a vasoactiveagent.

FIG. 5 is an exemplary waveform showing pulsatility of a signalassociated with arterial pressure of a patient.

FIG. 6 is an exemplary waveform showing heartbeats associated withpulsatility.

FIGS. 7 and 8 are exemplary patterns that can be used to detectdifferent vasoactive agents.

FIG. 9 shows a detailed flowchart of another embodiment for detecting avasoactive agent.

DETAILED DESCRIPTION

FIG. 1 shows the main components of a system that can be used toimplement the methods described herein for detecting a vasoactive agentin the bloodstream of a patient. Pressure, or some other input signalproportional to pressure, may be sensed either invasively ornon-invasively, or both. For convenience, the system is described asmeasuring arterial blood pressure as opposed to some other input signalthat is converted to pressure. Alternative systems can be used, as iswell understood in the art.

FIG. 1 shows both types of pressure sensing for the sake ofcompleteness. In most practical applications of the methods describedherein, either one or several variations can be implemented. In invasiveapplications, a conventional pressure sensor 100 can be mounted on acatheter 110, which is inserted in an artery 120 of a patient body part130. The artery 120 is any artery in the arterial system, such as, forexample, the femoral, radial or brachial artery. In the non-invasiveapplications, a conventional pressure sensor 140, such as aphoto-plethysmographic or a blood pressure probe, is mounted externallyin any manner, for example, using a cuff around a finger 142 or atransducer mounted on the wrist of the patient to read blood pressure ofan artery 144.

The signals from the sensors 100 and/or 140 are passed via any knownconnectors as inputs to a processing system 150, which includes one ormore processors and other supporting hardware and system software (notshown) usually included to process signals and execute code. The methodsdescribed herein may be implemented using a modified personal computer,or may be incorporated into a larger, specialized monitoring system. Foruse with the methods described herein, the processing system 150 caninclude, or is connected to, conditioning circuitry 152, which performsnormal signal processing tasks, such as amplification, filtering, orranging, as needed. The conditioned, sensed input pressure signal P(t)can then be converted to digital form by a conventionalanalog-to-digital converter ADC 154, which can take a signal referencefrom a clock circuit 156. As is well understood, the sampling frequencyof the ADC 154 can be chosen with regard to the Nyquist criterion so asto avoid aliasing of the pressure signal, which is known in the art ofdigital signal processing. The output from the ADC 154 can be thediscrete pressure input signal P(k), whose values may be stored inconventional memory circuitry (not shown).

The values P(k) can be passed to or accessed from memory by a software,hardware, or firmware module 160. For example, module 160 can comprisecomputer-executable code for calculating parameters associated with apulsatility of the pressure input signal. The pulsatility parameters canbe calculated at multiple points in time and can be any desiredparameter. Example parameters include pulse pressure, standard deviationof pressure waveform, systolic area, diastolic area, mean arterialpressure, systolic pressure, diastolic pressure, pressure at a specifictime point in each heartbeat, differentiation of pressure with respectto time, or a combination of these different parameters. If desired,patient-specific data, such as age, height, weight, BSA, etc., can bestored in a memory region 162 (other predetermined parameters, such asthreshold or threshold range values can also be stored). Predeterminedpulsatility data can also be stored in the memory region 162, so thatmeasurements can be based on historic patient data. Any of theabove-described values may be entered using any known input device 164in the conventional manner Detection of a vasoactive agent can beaccomplished in detection module 170. Detection module 170 can includecomputer-executable code that can analyze calculations made in module160 and perform the analysis for detection of a vasoactive agent, asfurther described below. As illustrated by FIG. 1, the results can bepassed to further modules 172 for additional processing. Alternatively,the additional processing can be performed within the detection module.In any event, the additional processing can include a calculation of ahemodynamic parameter. In such a calculation, whether or not avasoactive agent was present can be used. The hemodynamic parameter canbe associated with a wide variety of cardiovascular-related elements,such as cardiac output, stroke volume, systemic vascular resistance,stroke volume variation, cardiac index, stroke volume index, systemicvascular resistance index, vascular compliance, and vascular tone. Theresults can be displayed on a conventional display or recording device180 for presentation to and interpretation by a user.

FIG. 2 shows a flowchart of an exemplary method for detecting avasoactive agent. In process block 210, an input signal is received thatis associated with arterial blood pressure. The input signal can bereceived by an apparatus, such as is shown in FIG. 1, or other desiredapparatus, as is well understood in the art. The input signal can beproportional to, or derived from arterial pressure, flow rate, vascularresistance, pulse oximetry, Doppler ultrasound, bioimpedance signal, orrelated measurements or signals. The input signal can be in a variety offormats, such as a waveform, a digitized signal, or an analog signal. Inprocess block 220, a change of pulsatility is determined over a periodof time of the input signal. Pulsatility is generally known in the artto be a change in a pulse signal in response to each cardiaccontraction. The period of time can be any desired period. Some exampleperiods include any time between 1.0 and 60 minutes, but other timelimits can be used. In process block 230, a vasoactive agent can beautomatically detected using the measured change of pulsatility.Automatic detection can be achieved using hardware, software, orfirmware components, such as shown in FIG. 1. The vasoactive agent canbe a vasoconstrictor, a vasodilator, or an inotrope. Example vasoactiveagents include, but are not limited to Phenylephrine, Epinephrine,Ephedrine, Nitroprusside, etc.

FIG. 3 shows a flowchart of a particular embodiment that can be used todetermine a change of pulsatility and to detect the vasoactive agent. Inprocess block 310, a first parameter can be calculated at first andsecond times. A variety of parameters can be used. Example parameterscan include pulse pressure, standard deviation of pressure waveform,systolic area, or diastolic area. In process block 320, a secondparameter can be calculated at first and second times Like the firstparameter, a variety of parameters can be used, such as mean arterialpressure, systolic pressure, diastolic pressure, pressure at a specifictime point in each beat, differentiation of pressure with respect totime, systolic area, diastolic area, or a combination thereof. The firstand second times can be at any desired time interval apart.Additionally, the first and second times can be averages over first andsecond time periods. The process block 330 performs mathematicalcomparison of the first parameter and the second parameter. In oneexample, the mathematical comparison is performed by calculating theratio of the first parameter to the second parameter at the first andsecond times. Alternative waves to perform mathematical comparison couldbe used as well. The ratio can alternatively be the second parameter tothe first parameter. In process block 340, a difference between theratios at the first and second times is calculated. The difference orcomparison allows for a determination of how the ratio changes withrespect to time. In process block 350, a determination is made whetherthe calculated difference exceeds a predetermined threshold. Asdescribed further below, the presence of a vasoactive agent can resultin a change in arterial blood pressure parameters. The threshold allowsfor minor variations in such parameters to be ignored, whereas changesthat exceed a predetermined limit are indicative of the presence of avasoactive agent.

FIG. 4 is a flowchart of another embodiment, wherein detection is notnecessarily based on determining a change over time of an input signal.Rather, a parameter associated with pulsatility can be used to detectthe presence of a vasoactive agent. In process block 410, an inputsignal, such as a waveform, is received that is associated with anarterial blood pressure signal. The received waveform can be in avariety of formats, such as digital or analog data which when plottedrepresents a waveform. In process block 420, at least one parameterassociated with the pulsatility is calculated using the receivedwaveform. Calculation of such a parameter is well known in the art. Inprocess block 430, the vasoactive agent is detected using the calculatedparameter. Any of the above-identified parameters can be used in thecalculation. Moreover, any of the methods of FIGS. 2 and 3 can be usedto expand the method of claim 4.

FIG. 5 illustrates a sequence of measured or otherwise acquired arterialpressure waveforms over approximately three respiratory cycles. Inpractice, the sequence can be a data set P(k) derived from a sampledmeasurement of arterial pressure P(t). The P(k) values can be obtainedthrough direct, invasive or non-invasive measurement, or may be inputfrom some other source, such as from a remote monitor or even apre-recorded data set. Pulsatility can be calculated using one or moreof the following techniques on the received input signal: integralanalysis, correlation, Fourier analysis, maximum-minimum, derivative, orstandard deviation.

In FIG. 6, dots are included in the waveform of FIG. 5 to indicate thebeginning of each cardiac cycle (that is, each “beat”) over theillustrated computation interval. The beginning of each cardiac cyclecan be determined in any of a number of known ways using any knownsystem that is or includes a heart rate monitor. Assuming, for example,as is often the case, that the patient's cardiac electrical activity isalso being monitored by an electrocardiogram system (EKG), then thebeginning of each cardiac cycle may be determined to occur at thesampled pressure value immediately following each R-wave.Pressure-based, pulse-rate monitors may also be used and are in factpreferred because they will then be better synchronized with the bloodpressure signal than will, for example, an EKG signal.

FIG. 7 shows various input parameters that are graphed with respect totime, and various vasoactive agents that are indicated as being detectedat a time t, as soon as threshold values are reached. At 710, a graph isshown with mean arterial pressure (MAP) versus time. At 720, a heartrate (HR) parameter is shown versus time. At 730, a ratio of pulsepressure (PP) to MAP is shown versus time. As can be seen at 740, whenphenylephrine is introduced in the blood stream, the heart rate isrelatively unchanged, while the PP/MAP ratio decreases and the MAPincreases. Thus, using different pulsatility parameters, phenylephrinecan be identified. Additionally, analysis of such parameters can be usedto distinguish phenylephrine from other vasoactive agents. For example,introduction of epinephrine causes an increase in HR as shown at 750.Additionally, different parameters may have different thresholds. Forexample, dobutamine can be distinguished from epinephrine by looking atan amount of HR increase, as the HR increase for ephinephrine exceedsthat of dobutamine. Thus, using a combination of pulsatility parametersand/or threshold limits, it is possible to distinguish between differentvasoactive agents.

FIG. 8 shows an additional example of vasoactive agents that can bedetected using a variety of arterial blood pressure parameters. In thiscase, phenylephrine, epinephrine, ephedrine, and nitroprusside aredetected as being vasoactive agents present in a patient's blood usingone or more pulsatility-related parameters. For example, if MAPincreases above a predetermined threshold (as an absolute threshold or adifferential above a running average), it can be considered that avasoactive is present, although it can be difficult to know which one.Whereas if a second parameter is used, such as HR, a determination canbe made to distinguish phenylephrine from epinephrine. Other vasoactiveagents can be distinguished using PP/MAP or other parameters.

FIG. 9 shows a flowchart of a method of a detailed embodiment that canbe used. In process block 910, a blood pressure waveform is acquiredusing any of the above-described techniques. In process block 920, thewaveform can be divided into segments of predetermined durations (e.g.,20 seconds). In process block 930, each beat in a segment can bedetected, such as at the dotted points in FIG. 6. At process block 940,blood pressure related parameters are calculated for each beat. Exampleparameters are HR, MAP, PP, etc. In process block 950, the parametersare averaged over the segment. In process block 960, further parameterscan be calculated based on existing parameters. For example, a ratio ofPP to MAP can be calculated. Other ratios can also be calculated andused as parameters. In process block 970, a comparison is performedbetween current segment measurements and previous segment measurements.In process block 980, if the comparison exceeds a threshold, then avasoactive agent is present. For example, ifRatio_(current)<a*Ratio_(prev), HR_(current)=b*HR_(prev),MAP_(current)>c*MAP_(prev) then Phenylephrine is present at the currentmeasurement, wherein a, b, and c are predetermined constants. Ifdesired, a hemodynamic parameter can be calculated, wherein thecalculation includes using the presence or absence of the vasoactiveagent in the determination of the parameter.

Exemplary embodiments of the present invention have been described abovewith reference to a block diagram of methods, apparatuses, and computerprogram products. One of skill will understand that each block of theblock diagram, and combinations of blocks in the block diagram,respectively, can be implemented by various means including computerprogram instructions. These computer program instructions may be loadedonto a general purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions which execute on the computer or other programmabledata processing apparatus create a means for implementing the functionsspecified in the blocks.

The methods described herein further relate to computer programinstructions that may be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus, suchas in a processor or processing system, to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including computer-readableinstructions for implementing the described methods. Moreover, thevarious software modules used to perform the various calculations andperform related method steps described herein also can be stored ascomputer-executable instructions on a computer-readable medium in orderto allow the methods to be loaded into and executed by differentprocessing systems.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope of these claims.

We claim:
 1. A method for detecting a vasoactive agent in a patient'sbloodstream, comprising: receiving an input signal that is associatedwith arterial blood pressure; determining a change over time associatedwith pulsatility of the input signal; and automatically detecting avasoactive agent in the bloodstream using the determined change.
 2. Themethod of claim 1, wherein determining comprises measuring the changeassociated with pulsatility including calculating a first waveformparameter of the input signal at first and second times, calculating asecond waveform parameter of the input signal at the first and secondtimes, and calculating a ratio of the first waveform parameter to thesecond waveform parameter at the first and second times.
 3. The methodof claim 2, further including calculating a difference between theratios at the first and second times to obtain the measured change andwherein automatically detecting includes determining whether themeasured change exceeds a predetermined threshold.
 4. The method ofclaim 2, wherein the first waveform parameter is one of the following:pulse pressure, standard deviation of pressure waveform, systolic area,or diastolic area.
 5. The method of claim 2, wherein the second waveformparameter is mean arterial pressure, systolic pressure, diastolicpressure, pressure at a specific time point in each beat,differentiation of pressure with respect to time, systolic area,diastolic area, or a combination thereof.
 6. The method of claim 2,wherein the first waveform parameter and the second waveform parameterare exchangeable in the calculation of the ratio.
 7. The method of claim1, wherein determining comprises measuring the change associated withpulsatility by calculating a waveform parameter of the input signal atfirst and second times.
 8. The method of claim 7, further includingcalculating a difference between the waveform parameters at the firstand second times to obtain the measured change and wherein automaticallydetecting includes determining whether the measured change exceeds apredetermined threshold.
 9. The method of claim 7, wherein the waveformparameter is pulse pressure, standard deviation of pressure waveform,heart rate, mean arterial pressure, systolic pressure, diastolicpressure, pressure at a specific time point in each beat,differentiation of pressure with respect to time, systolic area,diastolic area, and a combination of any of those parameters.
 10. Themethod of claim 1, further including using that the vasoactive agent wasdetected in a calculation of a hemodynamic parameter.
 11. The method ofclaim 10, wherein the hemodynamic parameter is cardiac output, strokevolume, systemic vascular resistance, stroke volume variation, cardiacindex, stroke volume index, systemic vascular resistance index, vascularcompliance, vascular tone.
 12. The method of claim 1, wherein thereceived input signal is a waveform, and wherein the determining thechange includes dividing the waveform into segments of a predeterminedtime duration, detecting each beat in a segment, and calculating a pulsepressure and mean arterial pressure for each beat.
 13. The method ofclaim 12, further including averaging the pulse pressure and meanarterial pressure for all beats in a segment, calculating a ratio of theaverage pulse pressure to the average mean arterial pressure, andcalculating a difference in the ratio between multiple segments.
 14. Themethod of claim 1, further including calculating the pulsatility usingone or more of the following techniques on the received input signal:integral analysis, correlation, Fourier analysis, maximum-minimum,derivative, or standard deviation.
 15. The method of claim 1, whereinthe input signal is proportional to, or derived from one or more of thefollowing measurements: arterial pressure, flow rate, vascularresistance, pulse oximetry, Doppler ultrasound, or bioimpedance signal.16. The method of claim 1, further including measuring the arterialblood pressure invasively or non-invasively to produce the input signal.17. The method of claim 1, wherein the vasoactive agent is selected fromthe following: vasoconstrictor, vasodilator, or inotrope.
 18. The methodof claim 1, wherein determining includes receiving data associated withmeasuring a change over time of the pulsatility of the input signal. 19.The method of claim 1, wherein the input signal is a waveform, adigitized signal, or an analog signal.
 20. A method of detecting avasoactive agent, comprising: receiving a waveform associated with anarterial blood pressure signal; using the received waveform, calculatingat least one parameter associated with pulsatility of the arterial bloodpressure signal; and detecting a presence of a vasoactive agent usingthe calculated parameter.
 21. The method of claim 20, further includingmeasuring an average of the waveform over a period of time and whereindetecting the presence of the vasoactive agent includes detecting achange of greater than a threshold amount of the parameter.
 22. Themethod of claim 20, further including dividing the waveform intosegments of a predetermined period of time, detecting heart beats withineach segment, and calculating the at least one parameter for each beat.23. The method of claim 20, wherein the at least one parameter includesone of the following: pulse pressure, standard deviation of pressurewaveform, systolic area, diastolic area, mean arterial pressure,systolic pressure, diastolic pressure, pressure at a specific time pointin each heartbeat, differentiation of pressure with respect to time, ora combination thereof.
 24. The method of claim 20, further includingcalculating a hemodynamic parameter using the presence of the vasoactiveagent.
 25. The method of claim 20, wherein the at least one parameter isa first parameter that includes one of the following: pulse pressure,standard deviation of pressure waveform, systolic area, or diastolicarea and further including measuring a second parameter, which includesone of the following: mean arterial pressure, systolic pressure,diastolic pressure, pressure at a specific time point in each beat,differentiation of pressure with respect to time, systolic area,diastolic area, or a combination thereof.
 26. The method of claim 25,further including calculating a ratio comprising the first parameter andthe second parameter.
 27. The method of claim 25, wherein calculatingincludes using one or more of the following techniques: integralanalysis, correlation, Fourier analysis, maximum-minimum, derivative, orstandard deviation.
 28. The method of claim 25, further includingdetermining the first parameter at first and second times and the secondparameter at first and second times, and calculating a change over timeassociated with the first and second parameters.
 29. The method of claim25, further including determining a heart rate and differentiatingbetween different vasoactive agents using at least one of the first andsecond parameters in conjunction with the heart rate.
 30. A system fordetecting a vasoactive agent, comprising: a sensor that generates asignal corresponding to arterial blood pressure; and a processor forusing the signal to calculate a parameter corresponding to pulsatilityand analyzing whether a change in the parameter over time exceeds apredetermined threshold and, if so, calculating a hemodynamic parametertaking into account a presence of a vasoactive agent.
 31. The system ofclaim 30, wherein the parameter is a ratio comprising one of thefollowing: pulse pressure, standard deviation of pressure waveform,systolic area, or diastolic area and one of the following: mean arterialpressure, systolic pressure, diastolic pressure, pressure at a specifictime point in each beat, differentiation of pressure with respect totime, systolic area, diastolic area, or a combination thereof.
 32. Amethod for detecting a vasoactive agent in a bloodstream, comprising:receiving data associated with a blood-pressure parameter at a firstpoint in time; receiving data associated with the blood-pressureparameter at a second point in time; comparing the data at the first andsecond points in time; and based on the comparison, detecting a presenceof a vasoactive agent in the bloodstream.
 33. The method of claim 32,further including determining a type of vasoactive agent using thereceived blood-pressure parameter.